The invention relates to an arrangement for adjusting a characteristic, for example, picture brightness or contrast, of a picture displayed in a multi-window arrangement.
In a multimedia system, different sources of multimedia elements containing text, graphics, animation and motion video, respectively, are displayed on a display screen at different predefined regions in rectangular forms of different sizes, referred to as windows. Examples of windows are picture-in-picture (PIP), picture-outside-picture (POP) and picture-and-picture (PAP). The size of each window may be user adjustable on a window-by-window basis.
In a multi-window arrangement, the total light output of a displayed image is equal to the sum of the light outputs of each of the displayed windows that form an image. The total light output may be unequally shared between the displayed windows in a direct relationship to their concurrent picture contents. When the total light output is excessive, a window displaying a relatively dark picture might, disadvantageously, appear even darker than if the total light output were not excessive.
Television receivers or monitors having a cathode ray tube (CRT) usually include beam current limiting (BCL) arrangement. The BCL arrangement controls contrast and brightness levels of the video signals coupled to the CRT in order to limit the beam current for preventing excessive beam current. Thereby, the maximum light output of the CRT is limited by the BCL arrangement. Disadvantageously, the BCL arrangement reduces the contrast and brightness levels everywhere on the display screen of the CRT. As a result, a window having a dark picture, referred to as dark window, that does not contribute significantly to the total light output, would become, disadvantageously, even darker. There is a long felt need to readjust the light output produced in selective windows automatically, when the total light output of the display screen exceeds a predetermined level.
The light output attributable to each window can be calculated, for example, in accordance with the video signal that provides the picture information for display in the window and in accordance with the window area. When the total light output contributed by the windows exceeds the predetermined level, a loop controller automatically reduces, for example, the contrast and/or the brightness in selected windows, in accordance with a rule, in a loop control manner. The result is that the total light output drops below the predetermined level without necessarily making darker windows even darker.
A window presently selected by a user is referred to as an active window. All non-selected windows are referred to as inactive windows. More than one active window can be displayed at a given time. It can be desirable to exclude active windows from the automatic loop control adjustment.
In carrying out another inventive feature, the automatic loop control adjustment with respect to the active window is selectively disabled. Thereby, the contrast and/or brightness setting of the active window remains unchanged and unaffected by the automatic loop control adjustment. Selection of a new active window can automatically disable loop control in the newly active window and re-establish loop control in the previously active window.
Current flat panel displays such as Liquid Crystal Displays (LCD""s), Plasma Displays (PD""s) and Field Emission Displays (FED""s) do not have a BCL arrangement. It can be desirable to provide for the flat panel display an arrangement analogous to the BCL arrangement for the CRT for readjusting the light output produced in corresponding windows selectively and automatically.
In carrying out a further inventive feature, the automatic loop control derives information regarding the magnitude of the total light output by combining values of the video signal calculated with respect to each window. Thereby, advantageously, the automatic loop control adjustment can be utilized in flat panel displays.
The long felt need of the prior art is satisfied in accordance with the inventive arrangements.
A video display apparatus, embodying an inventive feature, includes a display device for displaying an image. A source of a plurality of input video signals containing picture information for display in a plurality of windows to form the image is provided. An arrangement for determining when a magnitude of a light output of the plurality of windows is outside a range of values and when the magnitude is within the range of values is provided. A signal processor responsive to the plurality of input video signals is provided. The signal processor generating therefrom a plurality of output video signals that apply the picture information for display in the plurality of windows, respectively. The signal processor is responsive to an output of the light output determining arrangement for automatically varying at least one of a brightness characteristic and a contrast characteristic of a first output video signal, associated with a first of the windows relative to that of a second output video signal, associated with a second of the windows, when the magnitude of the light output of the image is outside the range of values.